In the intricate architecture of the internet, data travels from one point to another through a set of rules known as protocols. Cybercriminals target TCP and UDP in Distributed Denial of Service (DDoS) attacks because these protocols sit at the core of almost all internet communication, making them high-leverage choke points. By overwhelming TCP’s connection-oriented handshake process or UDP’s connectionless, easily spoofed traffic flow, attackers can quickly exhaust server resources and disrupt availability with relatively little effort.
According to the November 2025 DDoS Analysis Report, high-volume UDP activity was the second most prevalent vector at 20.03%, while several TCP-based methods, including SYN, RST, and SYN/ACK amplification, remained consistently active.
To understand why attackers target these protocols, organizations should understand the similarities, differences, and use cases for UDP and TCP.
What Is TCP?
Transmission Control Protocol (TCP) is a connection-oriented protocol that serves as one of the main pillars of the Internet Protocol (IP) suite. Designed to provide reliable, ordered, and error-checked delivery of a data stream, it enables applications running on hosts to communicate over an IP network.
When an application requires a guarantee that every piece of data sent will arrive at its destination intact and in the correct sequence, TCP is the standard choice since it follows these steps:
- Establishing formal connections before transmitting any data.
- Managing the data flows.
- Closing the connection after completing the data transfer.
How Does TCP Work?
TCP uses several mechanisms to ensure reliability:
- Three-way handshake: Establishing a connection by having the client send a synchronize (SYN) packet then having the server respond with a synchronize-acknowledgment (SYN-ACK) packet before the client answers with an acknowledgement (ACK) packet.
- Data segmentation: Breaking data into smaller segments and assigning each a sequence number for later reassembly.
- Acknowledgement: Receiving an acknowledgement for each packet which, if not received, allows the sender to assume the packet was lost and retransmit it.
Additionally, TCP includes the following features that use the TCP header, a a 20-byte data structure containing source and destination ports, sequence numbers, acknowledgment numbers, and various control flags:
- Flow control: A “window size” mechanism that prevents a fast sender from overwhelming a slow receiver.
- Congestion control: A mechanism that uses perceived network conditions to dynamically adjust the rate at which data is sent to prevent the network from becoming overloaded.
What Is UDP?
User Datagram Protocol (UDP) is a connectionless communication model operating on a “best-effort” delivery principle, often described as “fire and forget.” UDP packages data into segments called datagrams then sends them to the destination without testing the connection first. Since it has minimal overhead, it offers high speed and low latency data transfer.
How Does UDP Work?
UDP follows this simple process for sending data:
- The application provides data.
- UDP attaches a minimal 8-by header, containing source port, destination port, the datagram length, and a checksum for basic error detection.
What are the Benefits of UDP and TCP?
Both protocols offer distinct advantages tailored to different application needs. The choice between them focuses on whether to prioritize data integrity data or delivery speed.
Benefits of UDP
The primary benefits of UDP stem directly from its simplicity and lack of overhead:
- Speed and Low Latency: By forgoing the three-way handshake and acknowledgment process, UDP significantly reduces latency, making it ideal for real-time applications that require immediate data delivery.
- Low Overhead: With a header size of just 8 bytes compared to TCP’s 20 or more bytes, UDP consumes less bandwidth per packet, making it efficient for high-volume traffic scenarios.
- Broadcast and Multicast Support: UDP’s connectionless nature means it can send multiple recipients data simultaneously using broadcast or multicast which is not natively supported by TCP’s one-to-one model.
- Application-Level Control: By offloading reliability concerns, TCP enables developers to implement their own custom error-checking and correction methods tailored specifically to their applications’ needs.
Benefits of TCP
TCP’s strengths lie in its comprehensive feature set designed for guaranteed data integrity:
- Reliability: TCP guarantees that data will be delivered to the destination, retransmitting data until the recipient successfully receives it.
- Ordered Delivery: By using sequenced numbers, TCP ensures that data is reassembled in the correct order at the destination which is essential for transferring files, loading web pages, or sending emails.
- Error Checking: TCP performs robust error checking using checksums on both the header and the data, ensuring that the received data has not been corrupted in transit.
- Congestion Control: TCP’s built-in mechanisms to detect and mitigate network congestion help maintain overall network stability, preventing a single connection from overwhelming shared network resources.
What Are the Drawbacks of UDP and TCP?
The protocols’ design choices also create inherent limitations that impact their suitability for different tasks.
Drawbacks of UDP
UDP’s drawbacks include:
- Unreliability: The protocol neither tracks nor resends packets, leading to lost data.
- No Ordering: UDP fails to track or re-order data which creates problems for applications that require sequential data processing.
- No Congestion Control: UDP lacks a built-in mechanism to slow down data transmission in response to network congestion, which leads to potentially flooded networks that can negatively impact other services.
- Vulnerability: UDP’s connectionless nature can make certain network attack types easier to deploy, like amplification attacks that spoof a victim’s IP address.
Drawbacks of TCP
TCP’s drawbacks include:
- Higher Latency: The three-way handshake and constant data segment acknowledgment process can slow down data transfer speeds by hundred of milliseconds.
- Greater Overhead: The larger 20-byte TCP header consumes more bandwidth per packet than UDP.
- Resource Intensive: Maintaining connection state, timers, and sequence numbers for each connection consumes more client and server memory and processing power.
- Head-of-Line Blocking: If one packet in a sequence is lost, all subsequent packets in that stream must wait for the lost packet to be retransmitted and received before they can be processed by the application, even if they have already arrived.
What Are the Similarities Between TCP and UDP?
Despite their fundamental differences, TCP and UDP have the following similarities:
- Transport Layer Operation: Both protocols operate at the OSI Model’s Layer 4, the Transport Layer, taking data from the application layer and passing it to the network layer.
- Use of Port Numbers: Both use port numbers to direct data to the correct application process on a host.
- IP Protocol Dependency: Both TCP and UDP run on top of the Internet Protocol (IP) which is responsible for routing packages from source to destination.
- Basic Data Integrity Check: Both protocols include a checksum field in their headers to check for data corruption that may have occurred during transmission.
What Are the Differences Between UDP and TCP?
The core differences between the two protocols define their respective roles in networking:
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- Connection: TCP is connection-oriented, establishing a dedicated connection using a handshake before transferring data while UDP is connectionless, sending data without any prior setup.
- Reliability: TCP is reliable, guaranteeing delivery through acknowledgments and retransmissions while UDP is unreliable, offering no guarantee of delivery.
- Ordering: TCP guarantees packet order using sequence numbers while UDP does not guarantee order.
- Speed: TCP is slower because its handshake, acknowledgements, and control feature introduce latency, while UDP is faster since it has minimal overhead.
- Header size: TCP has a larger, variable 20-byte header that can increase in size when using optional fields while UDP has a fixed 8-byte header.
Best Practices for Securing and Optimizing TCP and UDP Traffic
Many organizations use both TCP and UDP. To optimize and manage both types of traffic, organizations can implement these following best practices:
- Use protocol-aware DDoS protection: Ensure your defenses can distinguish between legitimate TCP/UDP behavior and malicious floods to maintain uptime during attacks.
Deploy anycast global routing for resilience: Distribute TCP and UDP traffic across a global footprint to absorb spikes and mitigate latency. - Implement intelligent traffic filtering and rate limiting: Apply adaptive rules tuned to protocol behavior, like SYN flood filtering for TCP and amplification-mitigation for UDP.
- Leverage authoritative DNS with built-in failover: Keep services reachable by pairing protocol-specific protections with highly available DNS resolution.
- Monitor protocol-specific anomalies in real time: Use deep visibility into TCP session states and unusual UDP patterns to detect threats before they escalate.
- Enable multi-vector threat detection: Use systems that correlate volumetric UDP floods, TCP state exhaustion, and application-layer anomalies across the stack.
- Test failover and throughput under protocol-specific load: Validate that systems behave correctly when TCP handshake pressure increases or UDP volume spikes.
UltraDNS and UltraDDoS Protect: Securing and Optimizing TCP and UDP Traffic
UltraDNS provides globally distributed, high-performance authoritative DNS that resists single points of failure, while UltraDNS² adds a second, fully independent DNS network for true redundancy. Together, they ensure fast resolution and continuous uptime, even during large-scale attacks or outages.
To further reduce risk, UltraDDoS Protect filters and scrubs malicious traffic before it reaches the network, stopping volumetric floods at the edge. For intelligent failover and load balancing, UltraDNS gives organizations the visibility, control, and stability needed to keep services running smoothly.
